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Graphene (G) can effectively enhance polymers' and polymer composites' electric, thermal, and mechanical properties. Nanofibrous mats have been demonstrated to significantly increase the interlaminar fracture toughness of composite laminates, hindering delamination and, consequently, making such materials safer and more sustainable thanks to increased service life. In the present paper, poly(ethylene oxide) (PEO), polycaprolactone (PCL), and Nylon 66 nanofibers, plain or reinforced with G, were integrated into epoxy-matrix Carbon Fiber Reinforced Polymers (CFRPs) to evaluate the effect of polymers and polymers + G on the laminate mechanical properties. The main aim of this work is to compare the reinforcing action of the different nanofibers (polyether, polyester, and polyamide) and to disclose the effect of G addition. The polymers were chosen considering their thermal properties and, consequently, their mechanism of action against delamination. PEO and PCL, displaying a low melting temperature, melt, and mix during the curing cycle, act via matrix toughening; in this context, they are also used as tools to deploy G specifically in the interlaminar region when melting and mixing with epoxy resin. The high extent of modification stems from an attempt to deploy it in the interlaminar layer, thus diluting further in the resin. In contrast, Nylon 66 does not melt and maintain the nanostructure, allowing laminate toughening via nanofiber bridging. The flexural properties of the nanomodifed CFRPs were determined via a three-point bending (3PB) test, while delamination behavior in Mode I and Mode II was carried out using Double Cantilever Beam (DCB) and End-Notched Flexture (ENF) tests, respectively. The lack of a positive contribution of G in this context is an interesting point to raise in the field of nanoreinforced CFRP. [ABSTRACT FROM AUTHOR]

Commercial, aromatic perylene diimide (PDI) dyes were used to exfoliate few-layer graphene nanosheets in low-boiling organic solvents such as chloroform and tetrahydrofuran. Importantly, in such solvents, graphene cannot be exfoliated in the absence of the aromatic perylene diimide (PDI) dyes. The PDIs are physisorbed onto the basal plane of the nanosheet surface, which stabilized them in solution; the aromatic core lies flat on graphene and the PDI side groups influenced the physisorption strength and molecular packing. Upon varying just a single atom in the chemical structure of the side groups, significantly different exfoliation efficiencies were observed. The graphene-PDI interaction was studied at the nanoscale by scanning tunneling microscopy and molecular dynamics, at the microscale by atomic force and electron microscopy, and at the macroscale by optical spectroscopy. Thanks to the high volatility of the chosen solvent, the nanosheets can be embedded in standard polymer composites through a simple solventinduced swelling procedure. [ABSTRACT FROM AUTHOR]

In the present study, the separation performance of new self-standing polyvinylamine (PVAm) membranes loaded with few-layer graphene (G) and graphene oxide (GO) was evaluated, in view of their use in carbon capture applications. PVAm, provided by BASF as commercial product named LupaminTM, was purified obtaining PVAm films with two degrees of purification: Low Grade (PVAm-LG) and High Grade (PVAm-HG). These two-grade purified PVAm were loaded with 3 wt% of graphene and graphene oxide to improve mechanical stability: indeed, pristine tested materials proved to be brittle when dry, while highly susceptible to swelling in humid conditions. Purification performances were assessed through FTIR-ATR spectroscopy, DSC and TGA analysis, which were carried out to characterize the pristine polymer and its nanocomposites. In addition, the membranes′ fracture surfaces were observed through SEM analysis to evaluate the degree of dispersion. Water sorption and gas permeation tests were performed at 35 °C at different relative humidity (RH), ranging from 50% to 95%. Overall, composite membranes showed improved mechanical stability at high humidity, and higher glass transition temperature (Tg) with respect to neat PVAm. Ideal CO2/N2 selectivity up to 80 was measured, paired with a CO2 permeability of 70 Barrer. The membranes' increased mechanical stability against swelling, even at high RH, without the need of any crosslinking, represents an interesting result in view of possible further development of new types of facilitated transport composite membranes. [ABSTRACT FROM AUTHOR]

It was previously proven that small loadings of few-layer graphene (G) and monolayer graphene oxide (GO) adjust the permselectivity and reduce the ageing of thick poly(trimethyl silyl propyne) (PTMSP) membranes, which currently inhibits their application in real separations. In this work, we extend the analysis to thin film composite membranes with top layers of PTMSP/G and PTMSP/GO between 1 and 7 µm. The good quality of the films, obtained by spin coating the polymer solution on porous flat supports, indicates that graphenic sheets are aligned parallel to the film surface, without defects, and that the large-scale production of such composite films is feasible. The addition of G and GO to PTMSP can improve the gas permeability and selectivity, and even change the behaviour from CO 2 -selective to He-selective. GO produces more repeatable effects than graphene, and it generally enhances the PTMSP permeability. The ageing was studied by tracking permeability of 4 gases with time: thin films age faster than thick ones, because ageing is due to free volume diffusion across the film. Incorporation of 1 wt% of G and GO visibly reduces the ageing of thin PTMSP films, and the effect is repeated on many different samples. The ageing can be correlated, with a single power law, to the ratio between time and squared film thickness. The exponent of such function, that quantifies the ageing rate, decreases when G and GO are added to PTMSP thin films, by factors as high as 40%. The temperature effect was studied, up to 60 °C, on annealed samples: the membranes, CO 2 -selective at room temperature, can become easily He-selective by raising the temperature. The He/CO 2 selectivity increases with temperature: such effect could be exploited syngas purification and pre-combustion capture processes. [ABSTRACT FROM AUTHOR]

Given the increasing relevance of poly(butylene succinate) (PBS) and poly( l -lactide) (PLLA) as bio-based thermoplastics, and the need to improve the properties of such polymers, a novel multicomponent reinforcing system was devised. Nanofibrous electrospun mats of PLLA containing graphene were incorporated into the PBS matrix via the conventional thermo-pressed molding technique. The final biocomposites were characterized in terms of morphological characteristics via SEM and STEM; TGA and DSC were used to investigate the thermal properties and tensile testing used to assess the mechanical properties. The results showed that PBS matrix does not have modified thermal behaviour in the presence of PLLA and graphene. On the contrary, the tensile strength of the composites was gradually enhanced with the addition of PLLA mats, and the improvement was found to be proportional to the number of PLLA layers and to the amount of graphene added. The huge potential of this multicomponent reinforcing system is highlighted by the 21% increment in tensile strength. [ABSTRACT FROM AUTHOR]